My friend John Stooke asks whether, being fully vaccinated, he is protected or not (SA, May 7). I'm afraid the answer can never be that simple. Vaccination protects over 90 per cent of people, but 100 per cent efficacy can never be achieved. So, yes, he has a 90 plus per cent chance of being protected, but if he is one of the remaining 8-9 per cent, he may still catch Covid – but he will certainly be less ill and far less likely to die. More importantly, does the vaccine stop transmission? The answer is not yet clear, but the evidence so far indicates that it stops it by at least 50 per cent – so there's a 50-50 chance that he may transmit it. And remember, vaccinated or not 30 per cent of people with Covid have no symptoms at all, so don't know they've got it.